Control cable system with improved compensating means



July 6, 1943.

' J. M. PITTS Fild Oct. 16, 1941 2 Sheets-Sheet 1 e e i F v f r I 1 a 2 S I 3 s= I 6; r NI 2 o to Q "3 D w Ava/Aria:

rroluvzys J. M. PITTS CONTROL CABLE SYSTEM WITH IMPROVED COMPENSATING MEANS Filed Oct. .16, 1941 2 Sheets-Sheet +1. 9 0% m6 -w Hw Y w/ -U Q ww Qvv Mm omw 9w 3 7 Hw m l uw Q Q I. mm I n I I m? 4 I s 7 lH Q mm ammy able force, as,

Patented July 6, 1943 CONTROL CABLE SYSTEM wrrn IMPROVED COMPENSATING MEANS Joseph M. Pitts, Dayton, Ohio Application 06mm: 16, 1941, Serial No. 415,2

(Granted under the act or March 3, 1883, as amended April so, 1928; 370 o. 6.757)

5 Claims;

The invention described herein may be manufactured and used by or for Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to control cables and particularly to control cables on aircraft.

In the operation of the several control elements on aircraft, and particularly those more remote from the pilot, it is common practice to provide cables, usually in pairs, for each element, the arrangement being such that putting one or the other of a pair of cables in tension moves the element to which they attach in one or the other direction of operation.

Due to the necessity of designing for lightness, control cables are made to a minimum di-v ameter consistent with safety, and are therefore subject to considerable stretching which necessitates adjustment of their lengths from time to time. Turnbuckles are usually provided for this purpose.

More recently, however, with the advent ofhigh altitude flying, a more serious difficulty has developed, particularly where the fuselage may be made of aluminum, or other material having a high rate of expansion per unt of temperature change, and the cables of steel, for in that case the temperature drop from ground to maximum altitude may be suillcient to cause the fuselage to shrink considerably more than the cables, with the result that control cables, adjusted with turnbuckles to the desired tenslon on the ground, may sag to such an extent at maximum altitude as to make control difficult if not dangerous.

The inventors of the various resilient take up means for control cables substantially all point to the above characteristic as desirable for,

' they say, if a great force is applied suddenly to Innumerable devices have been proposed to meet this situation and patents have been granted on many of them, but so far as is known they all consist, in some form or other, of a spring, so placed in some part of the length of the cable as to keep in under constant tension.-

Such an arrangement will, of course,-'take up the cable when it sags for any reason and will accordingly compensate for changes in the relative length of the ship and cable due to altitude.

But the trouble with using a spring to automatically keep a cable ,imder constant tension is that if the spring is made soft enough not to normally overstress the cabl it will yield upon application to the controlilever of any considerfor instance, when bringing a ship hard about or when executing a sharp loop or zoom, or, when pulling the ship out of a power dive.

the control lever, some part of the connecting means. between the lever and the control element should preferably yield at first then come back to normal gradually, so that a too rapid change of direction of the craft maynot stress some of the elements to the breaking point.

Designers of modern aircraft, however, and 'of war craft in particular, do not share the view that it is preferable to have a yieldable element in the control cable, where such yieldable element causes any lag in the response of a control element to the force applied to the control lever,

for in aerial combat, when it becomes necessary to execute a sharp change in direction, a lag in the response of the control element is more dangerousthan a momentary overstressingof the control cable.

Turnbuckles are therefore almost universally used for taking the slack out of control cables,

the turnbuckles being adjusted on the ground a at predetermined intervals and to a predetermined tension, but while this treatment of the problem solves it as far as slack due tocable stretch is concerned, it does not furnish any means for taking up the slack due to temperature change at high altitude.

It is therefore an object of this invention to provide a control cable arrangement in which a relatively soft spring keeps the slack out of a control cable at all times whether such slack is occasioned by stretching of the cables or by temperature changes at high altitude, but since such a spring is not strong enough but that it may yield upon sudden application of considerable force upon the control lever, such as would be required in executing a quick change in directlon, it is an additional object to provide means which will, upon application of such considerable force, lock the devicein the position to which the spring had previously adjusted it making it unyielding as would be the case hada turnbuckle been used for the adjustment.

- ployed.

J plied.

. temperature the piston in the cylinder space as within the cylinder and Figure 3 shows a compensator of modified form. t

Figure 4 shows a modified application of the inventionin which a single compensator is em- Like numerals refer to like parts throughout the drawings. 4

Referring more particularly to Figure 1, an

elevator I is hinged in the usual manner at I2 and has operating arms I8 and I8 extending oppositely from the hinge point. A control lever I8 is hinged at 20 and has operating arms 22 and 28 extending oppositely from its hinge point.

Control cables each comprising cable parts 28 and 28 connected by a compensator 80 are hinged to the outer ends of the arms I8, I8, 22 and 28 as at 82, 38, 38 and 38, whereby rocking of the control lever I8 about the hinge 20 rocks the elevator I0about' its hinge I2.

1 Referring more particularly to Figure the.

compensator 30 comprises a cylinder 80 threaded at 82 for the end cap 88. Ahub 88 extends from the end cap and. is

externally threaded at 88 for the packing nut 50 which bears against a packing gland 52 to compress the packing 58 around the rod 58 of the piston 58 which is axially slidable in the cylinder 80. The cable parts 28, 28 are joined to lugs 80, 82 on the ends of cylinder 80 and piston rod .58 respectively. A medium spring 88 urges the piston 58 toward the left, as seen in Figure 2,- with a force just suflicient to keep the cables taut. Such a spring is, of course, not stiff enough to resist being compressed upon sudden application of a considerable force tothe control lever I8 as is required in making a quick change indirection.

In order to prevent the spring 88 from yielding to compression upon application of a heavy force to the control lever I8, there is provided a valve meanswhich. freezes the piston in whatever po- 3i as in the preferred form 80,- The pistons,

however, are slightly different, that in the modification3l, being made in two parts 51 and 58 held together by"'screws 8|.

In the modification shown in Figure 4 an operating lever 88 and an operated arm I00 are held against stops" I02 and I08 by light springs I08 and I08. A connecting rod of considerable length IIO, together with a compensator 30, join the levers. The compensator maintains auto matic adjustment of the length of the rod H0,

to agree with the distance between its hinge points H2 and H8 which points may, of course, also vary from one minute to'the next due to temperature changes. The control system operates as follows: 4 Assume that an airplane equipped with the improved control cable system is on the ground and that the piston 58 is positioned in the cylinder 80 substantially as shown in Figure 2. If the plane now climbs, for illustration, to its maximum altitude,'the 'slack in the cables (see Figure 1) due to temperature change will allow'the spring 88 to move the piston 58 to the left and take up the slack, theamount of movement being depe dent of course upon the amount of the temperature change.

In-order to move to the left, the piston 58 must necessarily force a quantity of the hydraulic fluid from the space 80 through passages 88 and 18, through the small clearance between the ball 68 and its opening 88, through passages 80 and 88 into the space 82. I is Now since the clearance between the ball 88 and its opening 88 is very small, considerable time is required for the displaced fluid to pass from the space 80 to the space 82, but it also sition it may happen to have been adjusted by-.

the spring 88 This valve means consists of a ball 88 freely slidable in anopening 88 in a'rib I0 which is preferably, although not necessarily, integral with the cylinder 80. Cover members I2 and 18 are secured pressure tight to the faces of rib 10' by screws 18 and contain openings 18 and 80 for the'light springs 82 and 88, whilevsmaller passages 88 and 88 connect the openings 18 and 80 to the spaces 80 and 82 inside the cylinder 80. The opening 88 should be several one such that when on the ground and at average 58 will be near midway shown. The entire space the valve passages should be filled with a hydraulic fluid.

In the compensator shown in Figure 3, substantially the same effect is had as with that shown Figure 2, the only diflerence being in the m: 1 way which connects the end spaces 88 and 82 of the cylinder through the piston instead of around it. The ball 81, ball openin 88, Spring openings 18 and 8I for the light springs 83 and 85, and smaller openings 81 and 88 may be of the same diameter in the modified compensator at the time the heavy force is aptakes considerable time for the plane to climb toits maximum altitude, therefore the necessary volume of fluid will pass through the clearance space around the ball without disturbing its' position in its opening 88.. The clearance around the ball 88 is in fact such that the most rapid temperature changes that may occurin the plane and its cables will not shift more fluid fromspace 80 to'82 than may pass the ball 88 without moving it and compressing the light spring 88'. The

heavier spring 88 is therefore free to expand at the slow rate required to-take up cable slack due to temperature changes as well as slack due to cable stretch.-

If now,; while the cable is 'thus tautened, a necessity arises for applying a sudden heavy pressure .to the control lever I8 to execute -a quick change in direction, such. application will, upon an almost imperceptible movement of the piston 58 to the right, cause the ball 86 to compress the light spring 82 and seat itself against the seat 88, whereupon the piston 58 is frozen in its position inthe cylinder 80 and the compensator becomes a rigid member equal in effectivemess to a turnbuckle;

It will, therefore, be seen that, i the arrange- I mentshown and described, the effect is that of a spring take up for slack which is due to stretch nnii temperature change while the effectf'is that of a turnbuckle for resisting cable elongation during the application of heavy'pressure to the control lever. a

In themodification Figure 4, the spring I08 should preferably be stronger than the spring 88 in the compensator so that the lever I00 may always maintain its position against the stop I88. In other respects the action is the same as heretofore explained relative to Figure l.

Having thus described several variants of the invention, 1 claim: 1. An apparatus having an operable member, a spaced apart operating member, and connecting means operatively joining said members, said connecting means including a device for com-K pensating for lengthening or shortening of the other portions -ofthe connecting means, said de vice comprising in combination, a piston, a fluid filled cylinder closed around said piston, said piston being slidable in said cylinder, means for connecting said piston and cylinder to the other portions of said connecting means, there being a passageway connecting the spaces in said cylinder which are separated by said piston, and means for locking said piston; in situ in said :71- inder, said locking means comprising a valve in said-passageway which is normally sufliciently open to allow slow seepage of fluid from one end or the cylinder to the other, but is operative to be tightly closed by any rapid movement of fluid therethrough.

2. An apparatus having spaced apart operable and operating members with a connecting means operatively joining said members, said connectdevice comprising a piston, a fluid filled cylinder closing around said piston, spring means adapted to urge said piston axially in said cylinder, there being a passageway connecting the spaces in the cylinder which are separated by said piston, a-

valve in said passageway, a, second spring means normally biasing said valve to a position which a is suiliciently open to allow the'fluid tov seep through as the connecting means expands or contracts, but adapted to be closed against the resistance of said second spring'means by any rapid movement of said piston.

4. In a device having spaced apart operable members joined by a connecting means, a compensator in theconnecting means for automatically adjusting for expansion and contraction in said connecting means, said compensator ing means including a device for compensating for expansion or contraction of the other portions of said connecting means, said device comprising in combination, a piston, a fluid filled.

cylinder closed around said piston, said piston being slidablein said cylinder, means for joining piston and said cylinder to the other Dortions of said connecting means, there being a passageway connecting the spaces in said cylinder which are separated by said piston, and meansfor locking said piston in any position against movement in said cylinder, said locking means including a valve insaid passageway, a

light spring holding said valve in an open position, said valve when open being adapted to allow slowseepage only of fluid, from one end'of'.

said cylinder to the other, but adapted to be fully closed against'the resistance of said light spring when any considerable volume of fluid attempts to flow through said valve. a I

3. The combination, in a remote controlled apparatus, of a controlling member, a. spaced apart controlled member, means operatlvely connecting said members, an adjusting device included said connecting means, said adjusting I other, but adapted to compris n in combination, a fluid filled cylinder closed at the ends, a p ton slidable axially in said cylinder, a piston rod extending from said piston through one end of said cylinder,

means on the outer end otsaid rod and at the v.

opposite end on said cylinder for attachment in said connecting means, a resilientmeans' ur -v ing the piston away from the end from which the piston rod emerges, there being a passageway connecting the ends of the cylinder which are separated by the piston, a double check valve in said passageway biased to an open positionwhereby it willpermit slight seepage of fluid from either end of the cylinder. to the be closed tightly by movement of any considerable fluid from either end of the cylinder to the other, whereby rapid operation of said operable members locks said piston against endwise movement in said cylinder. 5; The structure, of claim 4 wherein the double check valve comprises a ball freely'sl dable in an opening comprising an enlarged section, of

said passageway said opening being of sufiicient' length to permit some endwise movement of said ball, smaller openings at each end or -saidball openings having seats for said ball at'their ends a 'which join the ball opening,'light springs under an initial stress for holding said ball midway in the length of the ball' opening, and still smaller openings extending from the spring openings to the spaces within the cylinder separated by the piston.

, JOSEPH PITTS. 

